The net investment income tax is a 3.8% U.S. tax on the lesser of net investment income or modified adjusted gross income above a filing-status threshold.
The net investment income tax (NIIT) is a 3.8% U.S. federal tax imposed on the lesser of an individual’s net investment income or the amount by which modified adjusted gross income (MAGI) exceeds the applicable filing-status threshold. A separate version applies to certain estates and trusts using undistributed net investment income and an annually determined income threshold.
NIIT is an additional tax layer. It does not replace regular income tax or capital-gains tax, and crossing an income threshold does not cause all investment income to be taxed at 3.8%.
For an individual:
This formula has two gates:
The smaller amount determines the NIIT base.
The IRS lists these statutory thresholds:
| Filing status | MAGI threshold |
|---|---|
| Married filing jointly | $250,000 |
| Qualifying surviving spouse | $250,000 |
| Married filing separately | $125,000 |
| Single | $200,000 |
| Head of household | $200,000 |
These thresholds apply to individuals; estates and trusts use a different computation. Filing status, residency, foreign-income adjustments, and specialized situations can change how MAGI is determined. Use the current Instructions for Form 8960 for an actual filing.
Net investment income is a tax-law calculation, not simply investment revenue minus all portfolio expenses.
| Income or gain | General NIIT treatment | Important qualification |
|---|---|---|
| Taxable interest | Commonly included | Tax-exempt interest generally is not included |
| Ordinary and qualified dividends | Commonly included | Regular income-tax rate classification still matters separately |
| Capital gains | Commonly included | Losses, basis, exclusions, and specialized gain rules affect the amount |
| Rental and royalty income | Commonly included | Nonpassive trade-or-business treatment can change the result |
| Nonqualified annuity income | Commonly included | Qualified retirement-plan distributions generally are excluded from NII |
| Passive trade-or-business income | Generally included | Material participation and activity classification matter |
| Financial-instrument or commodity trading business income | Can be included | Detailed trade-or-business rules apply |
Net gain means gain after applicable loss netting and tax adjustments, not gross sale proceeds. Selling securities for $500,000 does not create $500,000 of NII if their adjusted basis is $470,000; the starting gain is generally $30,000 before other adjustments.
The IRS identifies several common exclusions from NII:
An item excluded from NII can still increase MAGI. For example, wages are not net investment income, but wages can push MAGI above the threshold and thereby expose some NII to the tax. This two-part interaction is central to the calculation.
Assume a single filer has:
$235,000$28,000$200,000 NIIT thresholdFirst calculate excess MAGI:
Then compare net investment income with excess MAGI:
| NIIT-base component | Amount |
|---|---|
| Net investment income | $28,000 |
| MAGI above threshold | $35,000 |
| Smaller amount subject to NIIT | $28,000 |
The NIIT is:
The filer does not pay NIIT on all $235,000 of MAGI and does not use $35,000 as the base because NII is smaller. Regular income tax on the underlying interest, dividends, or gains is calculated separately.
If the same filer had $50,000 of NII, the NIIT base would instead be the $35,000 excess MAGI, producing $1,330 of NIIT.
MAGI measures income relative to the statutory threshold. NII identifies the investment-related tax base. Either one can be the limiting amount.
| Situation | NII | Excess MAGI | NIIT base |
|---|---|---|---|
| Below threshold | $30,000 | $0 | $0 |
| NII is smaller | $20,000 | $45,000 | $20,000 |
| Excess MAGI is smaller | $60,000 | $25,000 | $25,000 |
| No NII | $0 | $80,000 | $0 |
High MAGI alone does not create NIIT without NII. Investment income alone does not create NIIT when MAGI does not exceed the threshold.
Net investment income can be reduced by deductions properly allocable to included investment income, subject to the Form 8960 rules. Potential items can include investment interest expense, certain taxes, and other expenses attributable to NII, but regular income-tax treatment and NIIT treatment are not always identical.
Capital losses and carryovers can affect the net gain included in NII. Passive-activity losses, suspended losses, partnership items, and business deductions require their own ordering and limitation analysis. Do not subtract a personal expense or a gross investment-account fee merely because it relates generally to wealth management.
Recordkeeping should support:
Gain excluded from gross income under the federal principal-residence exclusion is not subject to NIIT. A taxable portion above an available exclusion may enter NII. The result depends on basis, qualifying use, ownership, depreciation, allocation, and other facts.
Rental income is commonly included in NII, but the treatment can differ when rental or business activity is nonpassive under the applicable rules. A real-estate label alone does not determine NIIT treatment.
| Tax concept | Tax base | Relationship to NIIT |
|---|---|---|
| Regular income tax | Taxable income under applicable rates | NIIT is calculated in addition to regular income tax |
| Capital-gains tax | Taxable net capital gain under applicable rate rules | A gain can affect both regular tax and NIIT |
| Additional Medicare Tax | Certain wages, compensation, and self-employment income above thresholds | Separate 0.9% tax; it does not apply to the same income category as NIIT |
| Self-employment tax | Net earnings from self-employment | Most self-employment income is excluded from NII |
| Estimated tax | Payment method during the year | May need adjustment to cover expected NIIT |
The phrase “Medicare surtax” is sometimes used informally for NIIT, but NIIT is separate from the Additional Medicare Tax. Use the formal tax name when reviewing a return or projection.
Certain estates and trusts calculate NIIT at 3.8% of the lesser of undistributed net investment income or adjusted gross income above the dollar amount where the highest estate-and-trust tax bracket begins. That threshold can change by tax year and is much lower than the individual thresholds.
Distributions, charitable deductions, grantor-trust status, exempt trusts, and beneficiary allocations can affect the result. Do not use the individual formula or thresholds for a trust return.
Start with projected adjusted gross income and make the NIIT-specific modifications required by Form 8960. Include wages and other income that can affect MAGI even when excluded from NII.
List included interest, dividends, annuities, rents, royalties, passive-business income, and net gains. Then apply properly allocable deductions and loss rules.
Large gains, business dispositions, installment payments, partnership allocations, option exercises, and Roth conversions can change MAGI or NII. Their NIIT effects cannot be inferred from cash proceeds alone.
NIIT increases total tax liability. The IRS notes that insufficient withholding or estimated payments can produce an estimated-tax penalty. Payment planning is separate from determining whether the tax applies.
3.8% to all investment income whenever MAGI crosses the threshold.The IRS NIIT overview provides the individual formula, thresholds, common income categories, and payment warning. IRS Tax Topic 559 summarizes individual and estate-or-trust treatment. The current Form 8960 and instructions control the detailed calculation and recordkeeping.
This article provides general financial education, not tax, legal, accounting, or investment advice. NIIT depends on tax year, filing status, residency, activity classification, basis, losses, deductions, entity structure, and other facts.